High pressure reinforced hydraulic hose is typically used on a variety of fluid power operated machines, such as earth-moving machines, to provide a flexible connection between several moving parts of a hydraulic circuit employed on or within the machine. Such hoses may include a hollow polymeric inner tube on which successive cylindrical layers of reinforcing material, such as wire or textile, are concentrically applied to contain the radial and axial pressures developed within the inner tube.
Many applications are demanding hose constructions with both high burst strength and long term fatigue resistance. Using conventional technology, the burst strength of a hose design may be increased by adding additional reinforcing material and/or layers, a practice which is generally discouraged because of its negative impact on the flexibility of the hose, or by universally increasing the tensile strength of each layer of reinforcement material, which may come at the expense of hose fatigue resistance.
To determine the robustness of a hose design, a hose manufacturer typically performs, among other tests, an impulse test and a burst test on the hose. An impulse test measures a hose design's resistance to fatigue failure by cyclically subjecting the hose to hydraulic pressure. A burst test, on the other hand, is a destructive hydraulic test employed to determine the ultimate strength of a hose by uniformly increasing internal pressure until failure. Based on these and other tests, a manufacturer can estimate a hose life that can be used to determine when a hose has reached the end of its life and may require replacing.
In some circumstances, it is desirable to detect, in a non-destructive and non-disruptive manner a likelihood of failure of a hydraulic hose. One solution providing this capability is discussed in U.S. Pat. No. 7,555,936, and discloses connecting a monitor circuit between two parallel, at least partially-conductive layers of a hose wall. A change in an electrical property observed by that monitor circuit may indicate a change in a property of the hose wall structure that might indicate impending failure of the hose wall.
To determine whether changes in electrical properties of a hose assembly have occurred, an electrical circuit is applied to the conductive layers of the hose wall. The results of testing such an electrical property (e.g., resistance) can be stored and/or communicated by the electrical circuit to a monitor remote from that electrical circuit. For example, when used in the context of a fluid power operated machine, a monitor can be located in a cab or other area where an operator can readily assess status of such hoses.
Because industries are increasingly centralizing controls of hydraulic systems to meet customer requirements in terms of compactness, as well as ease of use and maintenance, the electrical circuits positioned on hoses positioned away from the cab will not have a convenient, directly wired source of power. Accordingly, the electrical circuits used to monitor hose degradation are typically battery-powered.
Battery-powered monitoring circuits have a number of challenges. For example, due to the need for a small-sized package, generally the battery to be used must have a small form factor (e.g., coin-sized, or AA-size or less). These batteries generally have limited life spans, particularly when exposed to extreme environmental conditions (e.g., −40 degree Fahrenheit temperatures). Additionally, using batteries in applications where a hydraulic hose is difficult to reach causes difficulties, because then battery changes and other maintenance tasks become difficult. Accordingly, it is desirable to reduce an amount of maintenance that would be required of a monitoring circuit.
For these and other reasons, improvements are desirable.